The present invention relates to a latch device for a panic door lock and, more particularly, to a latch device for a panic door lock that provides a reliable anti-picking function.
A typical lock for a panic door generally includes a press bar that can be pressed to retract a latch for unlatching the door in emergency conditions as well as for normal passage. The lock can be locked to prevent unauthorized access and can be unlocked by a key from an outer side of the door. However, a burglar can pick the latch in the latching position. In an approach to prevent picking, the lock further includes a safety member that is pressed against by the door frame to a position releasing a stop piece when the door is closed. The stop piece, when released, is biased by a spring to a position in a retraction path of the latch. Thus, the latch can not be picked, for retraction of the latch is hindered by the stop piece. An example of such a lock is disclosed in U.S. Pat. No. 7,070,210 to Lin. However, the anti-picking function is lost when the spring fatigues, but the door can still be opened and closed. As a result, the users still use the door without noticing the risk of burglary.
Thus, a need exists for a panic door lock that provides a reliable anti-picking function.